This invention relates to operating means for a latch, for example a door latch.
A door latch set as conventionally used comprises an insert fitted in the free edge of the door between its front and back faces having a bolt which in its extended position protrudes beyond the edge of the door into a recess in the door frame and in its retracted position is wholly within the door to allow the door to be opened. The bolt is conventionally moved between its retracted and extended positions by rotation of an element of the latch set by rotation of a square section spindle extending through the door. Rotation of the spindle is usually effected by action of a door handle or knob on the spindle. The bolt will usually be spring biased to its extended position.
The bolt may be lockable in the extended or retracted position by a mechanism which prevents rotation of the handle or knob.
The door handles or knobs conventionally used in these arrangements need to be rotated by the user. There are users for whom and circumstances in which rotation is difficult, inappropriate or undesirable. Therefore efforts have been made to produce arrangements in which a linear rather than rotatory action by the user is required to move the latch bolt between its retracted and extended positions. One such arrangement is provided in UK Pat. No. 862871 in which a press member extends through the door and out of the door on both sides, the press member having inclined cam surfaces which act upon a formation on or connected with the latch bolt, linear movement of the press member causing the latch bolt to retract by a camming action, the latch bolt being spring loaded to the extended position. This arrangements suffers the disadvantage of not using a conventional latch set, and in that movement of the press member on one side of the door causes movement of the other end on the other side of the door.
A further suggestion utilizing a linear movement towards or away from the door to retract or extend the latch bolt is described in Swedish Pat. No. 348700, in which rotation of a conventional square latch spindle is achieved either by rotation of a handle or by pressure on the handle towards the door. In the pressure operated mode a pin and helical groove arrangement translates linear movement of the member carrying the pin into rotary motion of the member carrying the groove, the rotary motion being transmitted through the spindle to the latch set in order to open the door.
A still further suggestion operating on a very similar basis to that of Swedish Pat. No. 358700 is disclosed in UK Pat. No. 2070128 in which the door latch can be moved by pushing a push button. When the handle is pushed, it in turn pushes a drum bearing a pin. The pin engages a helical groove in a slug which is caused to rotate. The slug has a square-section bore through which the latch spindle passes and so the latch bolt is caused to retract.
The arrangements shown in UK No. 2070128 and Swedish Pat. No. 358700 suffer the disadvantage that operation of the mechanism on one side of the door has an effect on the other side of the door. Thus, the two operating actuators do not operate independently. Furthermore, these arrangements require a separate locking device if the door is to be locked.
As with the arrangements shown in UK No. 2070128 and Swedish Pat. No. 358700, the present invention is concerned with operating means intended particularly (but not exclusively) to operate conventional latch sets such as those falling within British Standard BS NO. 5872 (1980), the operating means using linear movement of an operating member towards or away from the door to cause rotational movement of a latch operating member by interaction of a thread on one member with a thread engaging cam on the other member.